With the increased efforts for the United States to become more energy independent, tapping the natural gas reservoirs throughout the United States has long been a viable solution. However, until recently getting to many of these reserves has been very difficult. Now through the development of horizontal drilling combined with hydraulic fracturing, sometime called “hydrofracking,” these reservoirs have become accessible. The drilling and fracturing techniques also raises Environmental concerns.
There is a need to develop and automate a sampling technique to address these energy and environmental concerns. The EPA has developed a sampling test method, called RSK-175, which outlines the testing procedure for Dissolved Gasses, practically for types of natural gas, including methane, ethylene, and ethane (as well as others). This EPA test method involves some manual preparation of the water samples. The manual preparation can be time consuming, along with problems in maintaining sample integrity; the person working with the field sample must open the sample vial to take measurements. This causes two sample integrity problems: (1) the contents of the opened sample vial are exposed to the atmosphere of the testing lab; and (2) the dissolved gasses in the water of the field sample can quickly escape into the testing lab, thereby significantly degrading the quality of the measurements of that sample.
More specifically, the field sample vials are full of liquid and have no headspace, and since there is a need to create a headspace for a dissolved gas analysis, the operator will open the sealed vial and pour off a volume of the liquid sample to create some headspace in the vial. Unfortunately, this exposes the headspace to atmospheric air and can contaminate the sample, or it can cause the compound of interest to be lost during that manual sample preparation.
A second manual way for sampling or analyzing dissolved gasses is to pour some of the liquid sample into a smaller headspace vial (such as a 22 ml vial), and then cap it and seal it, again with zero headspace. The user will then use a manual syringe to pierce the seal with two separate needles. In a dual piercing step, 5 ml of air or some inert gas is injected through a first needle into the vial, to force 5 ml of the sample out of the vial through a second needle. This will create a 5 ml headspace. This vial then will end up with two punctures of the seal, or a much larger single puncture if the needle was a dual-port concentric needle. Later, during equilibration, there could be some leakage because of the earlier punctures in the seal. Even later, during the sample inject step, the vial seal must be punctured yet again, with possible further leakage.
Another type of field sample vial can be full of liquid (again without a headspace) that need to be sampled and analyzed, in which the compounds of interest are in a liquid state at the outset. Such liquid compounds could be in a //mixture with water, or other naturally-occurring chemicals, or perhaps mixed with other man-made compounds. Using conventional techniques, a person would open the sealed vial and pour out some of the contents into a second vial, and leave a headspace portion in that second vial, for later partitioning and sampling. Unfortunately, this again exposes the sample to possible contamination, and further, some of the compounds of interest could be lost by “boiling” into a vapor phase, and escaping the vial altogether, before the second vial is sealed. This is likely when working with “lighter” volatile organic compounds (VOCs), i.e., VOCs having a fairly low boiling point at atmospheric pressure.
Therefore, a need for an automated process is warrant, especially one that maintains sample integrity for the dissolved gasses or other contaminants.